In the competitive marketplace which exists for automated surface-mount (SMT) electronics equipment, including systems for fabricating electronics equipment or components, improvements in accuracy and speed are a significant advantage. Such equipment is often used in fabricating, for example, semiconductor chips, printed circuit boards, liquid crystal displays, and thin film devices, and may feature multiple gantry/head assemblies, linear motors, photoimaging systems, etching systems, and/or a number of other technologies. The present invention relates to devices and methods for reducing vibration inherent in such equipment during operation thereby to improve the speed and/or accuracy of such equipment.
For example, modern photolithography tools require extremely high exposure accuracy. This can only be achieved if the levels of elastic displacement at crucial points in the tool do not exceed several nano-meters. Since lithography tools contain numerous moving parts such as the reticle and wafer stages, they are subject to persistent disturbing forces acting on their structure. Moreover, the tool structure is subject to environmental disturbances such as floor vibrations and air turbulence. While the level of these disturbances can be reduced, they cannot be eliminated in their entirety.
There are a number of existing techniques employed to limit the elastic vibration of lithography tools. For example, the stiffness of the structure that supports key elements such as the lens assembly may be increased, tuned mass dampers may be used, the signals applied to the moving stages may be shaped, or the floor vibrations may be isolated using actively controlled air springs. While effective in reducing elastic vibration, these methods often do not meet the stringent requirements of more advanced photolithography tools.
Current efforts to control vibration on SMT placement equipment include placing frictional damping device at the end of the gantry. This “friction block” serves mainly to stabilize the gantry and head trajectory control system, but it also has been shown to reduce the settling time during certain pick and place operations. However, the effectiveness of the friction block depends on precise tuning of the normal force (or pre-load). The friction block tends to wear out quickly, greatly reducing its effectiveness and contaminating the rest of the machine with particles. Moreover, the friction block works against rigid body movement, resulting in slower operation of the equipment. The vibration control system of the present invention, which comprises an actuator assembly, serves to replace the friction block entirely while improving settling time, or, alternatively, to operate in conjunction with the friction block, providing additional accuracy or speed of operation.
One aspect of the present invention relates to actuator elements useful for active vibration reduction, structural control, dynamic testing, precision positioning, motion sensing and control, and active damping. Electro-active materials, such as piezoelectric, electrostrictive or magnetostrictive materials, are useful in such tasks. In one embodiment of the invention, bare electro-active elements are used. In another embodiment, packaged electro-active elements, as described herein, are used.
Thus, improvements are desirable in the manner in which vibration is controlled in systems for fabricating electronic components, as well as the manner in which an actuator is attached to the equipment to be controlled.